This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The Universal Mobile Telecommunications System (UMTS) is a third generation (3G) mobile communication system which provides a variety of multimedia services. The UMTS Terrestrial Radio Access Network (UTRAN) is a part of a UMTS network which includes one or more radio network controllers (RNCs) and one or more nodes. The 3GPP is a collaboration of several independent standardization organizations that is focused on the development of globally applicable 3G mobile phone system specifications. The Technical Specification Group Radio Access Network (TSG RAN) is responsible for the definition of the functions, requirements and interfaces of the universal terrestrial radio access (UTRA) network in its two modes, frequency division duplex (FDD) and time division duplex (TDD). Evolved UTRAN (E-UTRAN), which is also known as Long Term Evolution or LTE, provides new physical layer concepts and protocol architectures for UMTS.
LTE is currently part of a work item phase within the 3GPP. One of the central elements of the system is a downlink control channel, which will carry all of the control information needed to assign resources for the downlink as well as the uplink data channels, where downlink and uplink conventionally refer to transmission paths to and from a mobile station and, for example, a base transceiver station. The elements for the control channel carrying allocation for the downlink channel, following the 3GPP 25.814 specification, can comprise at least: a resource allocation map describing the allocation map for physical resource blocks (PRBs); a modulation scheme/technique; a transport block size or payload size; Hybrid Automatic Repeat-reQuest (H-ARQ) information; multiple-input multiple-output (MIMO) information; and/or a duration of assignment.
3GPP Release 5 (Rel-5) introduced a new high speed downlink shared channel (HS-DSCH). In HS-DSCH transmission utilizing a H-ARQ system (a N-process stop-and-wait system), due to fact that different H-ARQ processes may require a different number of retransmissions, the medium access layer (MAC-hs) packet data units (PDUs) are not necessarily received in order by a desiring MAC-hs receiver. For example, two packets, packet 1 and packet 2, can be sent in consecutive transmission time intervals (TTIs). In this situation, it is possible that when packet 2 is received correctly by layer 1, the packet 1 may need further transmissions before it is correctly received and delivered to the MAC-hs layer of a user equipment (UE) receiver, thus leading to packet 2 getting to the MAC-hs before packet 1 during in-sequence delivery.
A physical downlink shared channel (PDSCH) can be used to carry the DSCH. In terms of considering PDSCH resource allocations, decisions in the 3GPP have gravitated towards using a circular buffer to implement rate matching between a turbo coded transport block and the amount of available physical resources. An issue related to the circular buffer technique has been described in a 3GPP contribution, R1-072273, entitled “Way Forward on LTE Rate Matching.” In this contribution, it was identified that in order to have good performance using the circular buffer technique, certain restrictions would be necessary, e.g., high redundancy version (RV) signaling granularity or limitations on the variability of the amounts of physical channel resources given to a single user for H-ARQ retransmissions. Therefore, both approaches can create additional problems in the form of either increased overhead or limited flexibility.
FIG. 1 illustrates an example of the circular buffer technique combined with H-ARQ using constant size resource allocation for H-ARQ retransmissions. According to FIG. 1, a transport block 100 is channel coded at 102 (omitting certain details such as cyclical redundancy check (CRC), tail bits, etc.). This provides, for example, three times the amount of bits, e.g., systematic bits 104, parity 1 bits 106, and parity 2 bits 108. The systematic bits 104 are interleaved at 110, resulting in interleaved systematic bits 114, while the parity 1 and parity 2 bits are parity bit interleaved at 112 resulting in interleaved parity 1 and parity 2 bits 116. According to the conventional circular buffer technique, the most important bits are taken for a first transmission 118, e.g., the systematic bits 114 and a first portion of the interleaved parity 1 and parity 2 bits 116. If reception of this first transmission 118 fails, a second transmission 120 is requested. For optimum operation of the conventional circular buffer technique, the second transmission 120 should take the coded bits that have not yet been transmitted, e.g., another portion of the interleaved parity 1 and parity 2 bits. Lastly, for a third transmission 122, the remaining non-transmitted bits are sent, and if excess capacity exists on the physical channel, additional systematic bits from the interleaved systematic bits 114 are transmitted (hence the circular buffer terminology). Therefore, as retransmissions are performed, the effective puncturing (omission of, for example, bits) is gradually reduced, such that after a given number of retransmissions, all the systematic and parity bits have been transferred for optimum decoder performance.
The example of transmission with circular buffering shown in FIG. 1 only illustrates a situation where the amount of physical resources is the same for each transmission attempt. With the need for frequency domain multi-user packet scheduling in LTE, a scenario will likely arise where H-ARQ retransmissions may not have access to the same amount of physical resources. Such a scenario is illustrated in FIG. 2, where the amount of physical resources for the second transmission is reduced, thus providing fewer parity bits for this particular H-ARQ retransmission.
Like FIG. 1, FIG. 2 shows a transport block 100 that is channel coded at 102 into systematic bits 104, parity 1 bits 106, and parity 2 bits 108. Interleaving of these bits occurs at 110 and 112, resulting in interleaved systematic bits 114 and interleaved parity 1 and parity 2 bits 116. The most important bits are taken for transmission at 118.
However, a problem arises when a second transmission 120 is lost in the receiver and the third transmission 122 is to take place. One possibility is to continue transmissions assuming that the physical resources are the same for each retransmission. This will cause “holes” in the received bit sequence, though, as shown in FIG. 2, where the third transmission 122 fails to transmit a certain portion(s) of the interleaved parity 1 and parity 2 bits. This effectively negates the “circular” property of circular buffering and penalizes H-ARQ performance (as compared to the conventional and idealized circular buffering scenario illustrated in FIG. 1). Alternatively, sufficient information could be provided at the starting point of the retransmitted data as shown by third transmission 124. However, this would require a high number of control channel bits for indicating this value.
Thus, in the presence of unequal resource allocation for retransmissions or an asynchronous H-ARQ protocol, a “signaled resource block (RB)” approach is required (either explicit or implicit), as is the case for 3GPP Rel-5 rate matching. While redundancy versions can be defined for circular buffer rate matching, it should be noted that doing so incurs the cost of losing the “circular” property of circular buffering, making circular buffering and Rel-5 (or Rel-5+Dithering) proposals equivalent from an H-ARQ perspective. That is, the circular buffer technique has not been utilized in previous 3GPP releases, and conventional signaling methods have only been designed for 3GPP Release '99 rate matching with RVs, level indicators, etc.